1. Field of the Invention
This invention relates to a driving system and actuator using an intercalation substance. More particularly, the invention relates to a driving system configured to convert a chemical energy supplied by using an intercalation substance directly into a mechanical energy and externally work with a driving force derived from the mechanical energy, which is suitable for application to technical fields of artificial intelligence robots, microelectronics, medical services, and so forth.
2. Description of the Related Art
Most of currently available actuators are electrically driven actuators, such as like electromagnetic motors and electrostrictive devices (piezoelectric devices), and those driven by fluid pressures, such as hydraulic actuators and pneumatic actuators. As far as they are used in various kinds of automated factory machinery and various kinds of transport machinery, existing actuators exhibit practically sufficient performances.
However, for use in autonomous robots under the need for emergent development, for example, actuators are required to operate with three-dimensional freedom of motion in cooperation with each other. In such cases, a force exerted by an actuator and its weight becomes a load to another actuator, and therefore, as the freedom increases, difficulty in controllability and total weight increase enormously. In these applications, muscle in living bodies can be said to be well-balanced actuators. In numerical values, displacement of living muscle is 50% in the direction of contraction, response time is 30 ms, developed tension is (2xcx9c10)xc3x97104 kgf/m2 (2xcx9c10 kgf/cm2), and maximum generated output is per unit weight is (0.1xcx9c0.3)xc3x97103 W/kg (0.1xcx9c0.3 W/g). No actuators satisfying these all have been developed yet (Applied Physics Vol. 60, No. 3 (1991), p. 258).
Polymeric gel is being remarked as artificial muscle similar to living muscle. Although some kinds of polymeric gel drives upon application of an electric field, generally employed are mechanochemical systems (or chemomechanical systems) that repeats swelling and contraction depending upon environmental changes such as temperature, pH, solution concentration, and so on, while converting chemical reaction energies directly to mechanical energies. Mechanochemical systems, themselves, employ living muscle as well, there are no examples in artificial substances other than organic polymeric materials such as polymeric gels, rubbers and collagen, for example (T. Takamori, xe2x80x9cActuator Revolutionxe2x80x9d, Kogyo-chosakai, 1987). Mechanochemical systems have a lot of advantages, such as being light, soft, and noiseless, and generating no exhaust gas by combustion. However, since most of currently developed polymeric materials are in amorphous states, and their structures have no anisotropy, they are interior in dynamic strength and durability.
On the other hand, most of inorganic layered materials represented by clay mineral are called intercalation materials, and can incorporate ions and molecules between layers by application of an electric field or chemical interaction. At that time, they change in lattice constant and volume. Therefore, these materials may become the third mechanochemical systems next to living muscle and polymeric materials.
As far as the Inventor is aware, as actuators using intercalation materials, there are currently those disclosed in:
Japanese Patent Laid-Open No. hei 02-131376
Japanese Patent Laid-Open No. hei 04-127885
Japanese Patent Laid-Open No. hei 05-110153
Japanese Patent Laid-Open No. hei 06-125120
Summarizing these actuators, the actuator disclosed in Japanese Patent Laid-Open No. hei 02-131376 has a structure sandwiching an electrolytic polyethylene oxide by graphite inter-layer compound such that flexion occurs by transpiration of Li between layers. The actuator disclosed in Japanese Patent Laid-Open No. hei 4-127885 is one of a series using Ag0.7V2O5 as its positive/negative poles and using 4AgI-Ag2WO4as its solid electrolyte. These actuators are such that ions are intercalated by application of an electric field and a change in volume is used as a driving force. Actuators disclosed in Japanese Patent Laid-Open No. hei 05-110153 and Japanese Patent Laid-Open No. hei 06-125120 are such that an electric field is applied from the exterior to a compound prepared by inserting a polar organic substance such as amine to an organic layered substance such as clay mineral, and displacement is obtained by changing the orientation angle of the organic substance existing between inorganic layers.
As reviewed above, all of conventional actuators using intercalation substances employ a driving system by application of an electric field and no reports have heretofore taught direct conversion of chemical energies to mechanical energies.
On the other hand, according to the knowledge of the Inventor, it can be expected that advanced actuators used in artificial intelligence robots or autonomous robots requiring drive portions having great freedom can obtain excellent properties that living muscle has.
However, as already discussed above, because it is only polymeric materials that conventional systems can be artificially made of, most of them are amorphous and their structures have no anisotropy, they have drawbacks in mechanical strength and durability.
It is therefore an object of the invention to provide a driving system using an actuator that uses an intercalation substance and becomes a new mechanochemical system removing those drawbacks.
Toward solution of the above-mentioned problems involved in the conventional techniques, the Inventor made researches and reviews that are summarized below.
As discussed above, all actuators using conventional intercalation substances were of types driven by application of electric fields. Through various reviews, the Inventor has come to the conclusion that the most suitable advanced actuator would be an actuator of a mechanochemical system using an intercalation substance and driven by converting chemical energies supplied by a solution directly into mechanical energies. This actuator is driven by a chemical technique, more particularly, by ingress and egress of a guest substance in and from a space between layers of an inorganic layered substance as a host substance due to chemical interaction by a supply of a solution from the exterior. This actuator can be configured as a muscle-shaped actuator (artificial muscle) creating giant displacement by using a single-crystal or c-axis-oriented film as the intercalation substance and stacking it in the c-axis direction that is the direction of expansion and contraction. Especially by using inorganic molecules having a large molecular length, giant displacement can be obtained more effectively.
The present invention has been made based the above-outlined reviews.
Toward a solution of the above-discussed problems, according to the invention, there is provided a driving system comprising:
an actuator using an intercalation substance and driven by exchange of solutions or by changing concentration of a solution; and
solution supply means for supplying the actuator with driving solution.
In the present invention, although the actuator is typically immersed in the solution supplied from the solution supply means, its entirety is not always in contact with the solution, but only a part thereof may be in contact with the solution. The solution contains a guest substance as explained later.
The actuator may comprise either a single element (module or unit) or a combination of a plurality of elements to obtain a desired size.
Basically, the actuator may have any shape, and it is designed in accordance with the purpose of its use. More specifically, the actuator may be in form of a cylinder or a prism having its axis in expansion and contraction direction of the intercalation substance, or a fiber. Preferably, for the purpose of its shape upon changes in distance between layers caused by intercalation reaction, the actuator is coated with an elastic, porous inorganic polymer that defines fine holes permitting the solution to pass through, at least on a part of the side surface, or typically on the entire surface. The coating, however, may be omitted. The actuator typically has a structure in which a plurality of cylindrical, prismatic or fiber-shaped elements are serially connected, or a structure in which a plurality of the said structures each serially connecting a plurality of cylindrical, prismatic or fiber-shaped elements are connected in parallel(or bound together). For the purpose of not preventing expanding and contracting actions, individual elements are integrally coupled by bonding or other means.
The actuator may have a form of a film or plate in which the expanding and contracting direction of the intercalation substance is vertical to the major surface. Preferably, for the purpose of maintaining its shape upon changes in layer-to-layer distance caused by intercalation reaction, the actuator is coated with an elastic, porous inorganic polymer that defines fine holes permitting the solution to pass through, at least on a part of the side surface, or typically on the entire surface. The coating, however, may be omitted. The actuator typically has a structure in which a plurality of film-shaped or plate-shaped elements are serially connected, or a structure in which a plurality of the said structures each serially connecting a plurality of film-shaped or plate-shaped elements are connected in parallel (or bound together). For the purpose of not preventing expanding and contracting actions, individual elements are integrally coupled by bonding or other means.
The actuator may be made of an element made by shaping powdered intercalation substance into a predetermined shape. Preferably, for the purpose of its shape upon changes in distance between layers caused by intercalation reaction, the actuator is coated with an elastic, porous inorganic polymer that defines fine holes permitting the solution to pass through, at least on a part of the side surface, or typically on the entire surface. The coating, however, may be omitted. The actuator is typically mad up of a structure in which a plurality of elements each made by shaping a powdered intercalation substance are connected in series, or made up of a structure in which a plurality of the said structures each made up of the serially connected elements each made by shaping the powdered intercalation substance are connected in parallel (or bound together). For the purpose of not preventing expanding and contracting actions, individual elements are integrally coupled by bonding or other means.
Alternatively, the actuator may be made by bonding an intercalation substance around a tubular hollow member of an elastic material defining fine holes permitting the solution to pass through such that the expanding and contracting direction of the intercalation substance is parallel to the axial direction of the hollow member. In this case, the solution is supplied into interior of the hollow member from the solution supply means. Subject to the purpose of its use, a hollow yarn, for example, may be used as the hollow member.
The actuator may be made by appropriately combining various types of elements mentioned above, depending upon the purpose of its use.
The actuator may have a bimorph structure in which a first actuator using a first intercalation substance and a second actuator using a second intercalation substance are bonded vertically to the expanding and contracting direction of the first intercalation substance and the second intercalation substance, or a unimorph structure in which an intercalation substance the an elastic member are bonded vertically to the expanding and contracting direction of the intercalation substance. In the former case, the first and second intercalation substances may be either identical or different. Between the first actuator and the second actuator, an elastic member (such as organic polymeric material like a fluorine-series resin or a metal like Pt), for example, may be interposed. These may be used also as the elastic member in the latter case.
The solution supply means is preferably configured to supply the solution to the actuator while recovering and reusing the solution. In other words, it is configured to circulate the solution. Alternatively, the solution supply means may be configured to supply the solution to the actuator while replacing at least a part of the solution by a corresponding amount of fresh solution.
Typically, the actuator is contained in a container, and the solution supply means includes at least one solution supply tube connected to one or the other end of the container to define a closed path passing through the container. Normally, a plurality of the solution supply tubes are provided such that different solutions can be supplied. Preferably, a drainage treatment portion (drainage refiner) is provided enroute of these solution supply tubes to refine solution discharged from the container and from a pump for sending solution to the container. The drainage treatment portion refines solution by ion exchange, for example.
In a typical example, the solution supply tube includes a first solution supply tube for supplying a first solution which expands the intercalation substance and a second solution supply tube for supplying a second solution that contracts the intercalation substance. In this case, to enable switching of the solutions to be supplied to the container, the first solution supply tube and the second solution supply tube are normally connected to one and the other ends of the container via control valves controlled in opening and closing motions in response to expansion and contraction of the actuator.
The actuator may be used in combination with one or more such actuators, depending upon the way of its use. For example, a first actuator and a second actuator may be used as the actuator such that these first and second actuators share a common support and antagonistically expand or contract.
In the present invention, the actuator is basically applicable to any purposes provided they use expanding and contracting movements. However, from the viewpoint of flexibility and litheness of movements, application to artificial muscle is suitable. Especially, when the first actuator and the second actuator share a common support for antagonistic movements, the actuator provides movements similar to those of living muscle.
In the present invention, the host substance of the intercalation substance is typically a substance containing at least one kind of inorganic layered substance whereas the guest substance of the intercalation substance is ions or molecules such that ingress and egress of the guest substance in and from a space between layers of the inorganic layered substance as the host substance change the layer-to-layer distance and there by drives the actuator. The host substance may be an inorganic/organic composite substance that comprises an inorganic layered substance as its matrix, and at least one kind of organic substance intercalated between layers of the inorganic layered substance such that the host substance is changed in distance between its layers by ingress and egress of a guest substance and thereby drives the actuator. Typically, the host substance immersed in a solution containing the guest substance, and by replacement of the solution containing the guest substance with a solution not containing the guest substance, or by changes in concentration of the solution containing the guest substance, reversible egress and ingress of the guest substance relative to a space between layers of the host substance change the distance of the space between the layers and thereby activate the actuator. The guest substance is typically an organic substance, and particularly an organic material having at least one polar functional group in at least one of its carbon positions. Substances having this feature are ammonium, amine, aniline, amino acid, uric acid, alcohol, hydrazine, aldehyde, acetone, acrylonitrile, sugar, pyridine, phosphine, ethylene oxide, and so on.
The inorganic layered substance as the host substance may be, for example, at least one kind of substance selected from the group consisting of layered perovskite, niobium-series substances, layered perovskite copper-series substances, layered titanium niobates, layered halite oxides, transition metal oxides bronze-series substances, transition metal oxochlorides, layered polysilicates, layered clay minerals, hydrotalcites, transition metal chalcogenides, phosphoric acid zirconates and graphite. Specific examples of these substances are shown below.
(1) layered perovskite niobium-series substances:
KLaNb2O7, Kca2Nb3O10, RbCa2Nb3O10, CsCa2Nb3O10, KNaCa2Nb4O13 
(2) layered perovskite copper-series substances:
Bi2Sr2CaCU2O8, Bi2Sr2Ca2Cu3O10 
(3) layered titanium niobates KTiNbO5, K2Ti4O9 or K4Nb6O17 
(4) layered halite oxides:
LiCoO2, LiNiO2 
(5) transition metal oxide bronze-series substances:
MoO3, V2O5, WO3, ReO3 
(6) transition metal oxochlorides:
FeOCl, VOCl or CrOCl
(7) layered polysilicates:
Na2O-4SiO2-7H2O
(8) layered clay minerals:
smectite, vermiculite, mica
(9) hydrotalcites:
Mg6Al2(OH)16CO3xe2x80x94H2O
(10) transition metal chalcogenides:
TaSe2, TaS2, MOS2, Vse2 
(11) phosphoric acid zirconates:
Zr (HPO4)2nH2O
(12) graphite:
C
In the present invention, an acidic solution and/or alkali metal hydroxide solution are typically used for disconnecting the guest substance from the host substance. Usable as the acidic solution are hydrochloric acid, nitric acid, fluoric acid, sulfuric acid, and soon. Usable as the alkali metal hydroxide solution are KOH and others. Especially when the guest substance is amine, the use of hydrochloric acid is effective for disconnecting the guest substance from the host substance.
According to the driving system proposed by the invention having the above summarized structure, since it uses the actuator using an intercalation substance and driven by switching solutions or changes in concentration of a solution, it is possible to obtain a driving system of a mechanochemical system that converts chemical energy directly to mechanical energy to use it as a driving force.